In its most widespread configuration, a pumping installation comprises a wellhead equipped with a surface bearing drive mounted on a “blowout preventer” remotely driving a progressing cavity pump mounted at the base of a production string or inserted into the production string. The pump is installed downhole. The bearing drive, at the wellhead, supports and drives in rotation a drive shaft called a “polished rod”. The polished rod drives a drill string (or a continuous pipe) located inside and throughout the length of the production string. This drill string in turn drives in rotation the rotor of the progressing cavity pump situated downhole. The fluid, situated downhole, is transferred through the pump and delivered into the production string up to the wellhead, from where it is evacuated by distribution pipes. The torque anchor holds the stator of the pump in such a way that it is not itself driven in rotation downhole and thus prevents the disconnection of the tubing forming the production string.
Torque anchors are known, in particular from the document U.S. Pat. No. 6,155,346, for a pumping installation, comprising teeth mounted on a cam, fixed to the tubing string. The teeth are suitable for being moved, via the cam, between a retracted position within the torque anchor and a blocking position in which the teeth extend radially outside the body of the torque anchor and grip the casing.
Such torque anchors have numerous disadvantages.
Firstly, they are based on interference techniques, and are therefore likely to become dislodged during production due to the strong vibrations generated by the progressing cavity pump. This dislodging can lead to the tubing string becoming unscrewed and falling downhole, involving a complete shutdown of the production operations and a significant cost for carrying out fishing operations.
Then, in certain cases, the retraction mechanism can become clogged due to the presence of sand, or be degraded by corrosion. In this case, the torque anchor is raised by force so that the casing and the downhole equipment are damaged.
Furthermore, the teeth are brought into blocking position by the rotation of the tubing string from the surface, carried out by operators using grip wrenches. This driving operation presents a certain risk to the safety of the operators handling the grip wrenches in order to impart a torsional stress. In fact, when the grip wrench slips, it can injure the operators.
Moreover, in normal operation, the interference of the teeth in principle leads to extremely high contact pressures between said teeth and the casing. Thus, given the high level of vibration during pumping, it is strongly suspected that the teeth, the form of which is necessarily aggressive in order to initiate interference, “machine” the casing.
Moreover, certain wells are subjected to significant variations in temperature during production. These temperature variations expand the tubing string which can be extended by a length of up to 6 meters, but do not expand, or only slightly expand, the casing since this is cemented to the formation. During these temperature variations, the torque anchor, pushed by the expansion of the production string, is displaced relative to the casing along the longitudinal axis of the well. As the teeth of the torque anchor are still anchored in the casing, definite damage caused by notching of the inner wall of the casing is suspected but has thus far not been quantified.
Finally, in order to be sure that the teeth of the torque anchor are firmly gripping the casing, they can be driven into blocking position at the surface of the well before the torque anchor is lowered downhole. In this case, the casing pipe assembly is cut and damaged during the descent of the torque anchor downhole.
The document EP 1 371 810 describes an anti-rotation device for a drilling rig of the type comprising a rotatable shaft and a housing containing the rotatable shaft. The anti-rotation device is suited to blocking the rotation of the housing in the wellbore. It comprises carriages provided with rollers mounted on a shaft perpendicular to the longitudinal axis of the housing. The edge of the roller is tapered so as to engage the rock of the wellbore and, by means of this engagement, to prevent any rotation of the drilling rig.
However, this anti-rotation device is not suitable for use in a casing as the tapered surface of the rollers risks cutting and damaging the casing. Furthermore, this device is undersized with respect to the torsional stresses applied by a stator to the production string, when the rotor is driven in rotation. Such a device could only counter such stresses by increasing its size in such a way that it could no longer be inserted into the production string.